Nondeterministic time dependent mechanics of elementary prestressed and cable stayed concrete bridges models

The time dependent behaviour of two elementary structures, one made of a concrete cantilever beam, suspended at the tip by a pretensioned stay, and the other made of a concrete cantilever beam, post-tensioned through a horizontal cable, has been studied. After a short recall, which would outline how a suitable stay pretensioning or a suitable cable post tensioning, may balance the deflections due to selfweight only under elastic hypotheses, the effects of creep on the tip vertical displacement and on the tension in stay are studied. The influence on such effects, due to different stay slopes, is discussed. As well known, the data needed for these analyses involve many uncertain quantities. Thus, in a second part of the paper, through a probabilistic approach, the effects due to large variations of the tension in the cable are studied. On the basis of the achieved results, we can distinguish between two different kinds of structures: those which have a low sensitivity and those which are greatly affected both by creep effects and by uncertainties.